Red lines, Red ring, Black ring, Red/black ring, Red blob, Red/black blob, and White. Genetic factors underlying color morphs These color polymorphisms follow simple Mendelian genetics. The most common morph is Yellow, which makes up 70% of populations. Genetic studies of these morphs have shown that the Yellow morph, which is also known as the "unpatterned" morph, is recessive to all patterned morphs. Within patterned morphs, the amount of pigment present in the abdomen is correlated with the dominance of the associated allele. The alleles that are associated with black, red, or white pigments are arranged in a hierarchical structure and exhibit dominant effects. In addition, unpatterned morphs are recessive to patterned morphs. Lastly, White is dominant to nearly all morphs. The White morph is produced by a massive deposit of guanine below the hypodermis, a structure derived from the ectoderm. The presence of this white background is beneficial when bright-colored morphs are advantageous. Guanine is the main nitrogenous excretory product in spiders. These deposits create a white background between the brown digestive diverticula, a structure of the midgut, and the hypodermis. These guanine deposits and their distribution within the body are under the control of a major gene loci in T. grallator. This major gene loci is under the control of two mechanisms. These two mechanisms respond to the presence or absence of guanine and send chemical signals between the hypodermis and digestive diverticula to adjust morph pigmentation. In addition, these two mechanisms may function independently or together. The first mechanism operates by inhibiting the effect of guanine on pigmentation; thus, unpigmented areas will contain a layer of guanine beneath. The second mechanism operates by inducing guanine with light, resulting in guanine deposits present under unpigmented areas. Guanine is found only under the red and black hypodermal pigments that form the various morph patterns. White and Red lines exhibit codominance. There appears to be no sex-linkage in the distribution of morphs between sexes. Theridion grallator is known for its exuberant carapace and opisthosoma (abdomen) patterning. Opisthosomal morphs appear to be dictated by alleles at one autosomal locus. Dominance typically comes from superimposing one pattern over the other. The linkage between loci may be responsible for the association between carapace and opisthosomal patterns. Although there is a possibility of pleiotropic effects of alleles at one particular locus, it is not likely given the associated patterning on the carapace and abdomen.